The present invention generally relates to video signal processing apparatuses, and more particularly to a video signal processing apparatus which processes a video signal which is transmitted in accordance with a dot interlaced scanning system, without deteriorating the picture quality even when the original picture is a moving picture.
Generally, when an attempt is made to record and reproduce in an apparatus such as a video tape recorder (VTR) for home use having a relatively narrow recording and reproducing frequency band a video signal having a relatively wide frequency band of approximately 4.2 MHz, for example, the video signal becomes greatly attenuated especially in the high frequency band. As a result, the picture quality becomes deteriorated. Accordingly, the frequency band of the video signal must somehow be compressed at the time of the recording performed in the VTR and then expanded at the time of the reproduction performed in the VTR in order to prevent the picture quality from becoming deteriorated.
Between the luminance signal and the carrier chrominance signal of the video signal, it is the luminance signal that has a greater effect on the picture quality with respect to the human eye. For this reason, the luminance signal occupies a wider frequency band. Hence, the frequency band of the video signal can be compressed effectively by compressing the frequency band of the luminance signal.
In a television picture, an interlaced scanning takes place. Odd lines of the picture are scanned during an odd field and even lines of the picture are scanned during an even field. In other words, a picture corresponding to one frame is made up of an odd field and an even field. Generally, data related to all of the picture elements in one line are transmitted during one horizontal scan. However, according to a known dot interlaced scanning system, only the data related to every other picture elements in one line are sampled and transmitted during one horizontal scan, and as a result, the frequency band is compressed by 1/2. In other words, according to the dot interlaced scanning system, the data related to every odd numbered picture elements in each odd line are sampled and transmitted during the odd field and the data related to every even numbered picture elements in each even line are sampled and transmitted during the even field, for example. However, because only the data related to every other picture element in each line are sampled and transmitted according to the dot interlaced scanning system, the frequency band is reduced by 1/2 but the horizontal resolution becomes reduced by 1/2. Thus, there is a disadvantage in that the horizontal resolution becomes deteriorated according to the dot interlaced scanning system.
Therefore, a system of carrying out the dot interlaced scanning in terms of four fields was previously proposed so as to overcome the disadvantage of the dot interlaced scanning system. According to this previously proposed system, picture element data which correspond to one field and in which the picture element data of the first and third dot interlaced fields alternately exist on each line are transmitted during a time period of one field, and picture element data which correspond to one field and in which the picture element data of the second and fourth dot interlaced fields alternately exist on each line are transmitted during the next time period of one field, as will be described later on in the specification in conjunction with the drawings. However, according to this proposed system, the picture element data corresponding to one field are made up of the picture element data of the first and third fields (or second and fourth fields), that is, the picture element data of two different fields. Thus, no problems are introduced in the case where the original picture is a still picture. But when the original picture is a moving picture, a double picture is obtained, and there is a disadvantage in that the picture quality is greatly deteriorated. The double picture is a picture in which an image such as an automobile, for example, is displayed at two mutually shifted positions.